const int LED_Pins[4] = {0,4, 9,13};  // Pins connected to the LEDs

void setup() {
  // Set LED pins as OUTPUT
    for (int i = 0; i < 4; i++) {
        pinMode(LED_Pins[i], OUTPUT);
          }
          }

          void loop() {
            // Display numbers from 0 to 15 and their complements
              for (int number = 0; number <= 15; number++) {
                  displayBinary(number);
                      delay(1000);  // Delay 1 second

                          displayBinary(~number & 0x0F);  // Display complement
                              delay(1000);  // Delay 1 second
                                }

                                  // Wait for 2 seconds after reaching 15
                                    delay(2000);
                                    }

                                    // Function to display a decimal number in binary on LEDs
                                    void displayBinary(int num) {
                                      for (int i = 0; i < 4; i++) {
                                          digitalWrite(LED_Pins[i], (num & (1 << (3 - i))) != 0);
                                            }
                                            }